To form bright, beautiful blooms,
plants such as gladioli and roses need to be protected against diseases, weeds,
nematodes, and other natural enemies.

To provide that protection, growers often fumigate their fields before
planting. The fumigant of choice? Methyl bromide, one of American agriculture's
most widely used and most reliable farm chemicals.

In fields where blooms will be produced for the cut-flower market, growers
typically apply methyl bromide plus chloropicrin, a combination that zaps
soilborne pathogens and weed seeds.

Methyl bromide is being phased out,
however, because of indications that it depletes Earth's ozone layer. The layer
shields usand other living thingsfrom harmful doses of ultraviolet
radiation.

To help growers of cut flowers cope with the impending loss of this widely used
fumigant, ARS scientists in California
and their university colleagues are working with flower growers to test an
array of promising alternatives. The California Cut Flower Commission, based in
Watsonville, is helping coordinate the research.

Propargyl bromide is among the chemicals that might be used in place of methyl
bromide.

"Even though propargyl bromide is not new," says ARS agricultural
engineer Thomas J. Trout, "little is known about it. And, it isn't
registered by the U.S. Environmental Protection Agency for use as a
pesticide."

To find out more about this
fumigantfastthe U.S. Department of Agriculture recently allocated
more than $1 million to finance ARS and university research on the compound.
Trout, who leads the ARS Water Management Research Unit at Fresno, California,
is coordinator of a cluster of USDA-funded propargyl bromide studies, including
university investigations into its use as a preplant fumigant for floral crops.

Weed scientist Clyde L. Elmore and plant pathologist James D. MacDonald of the
University of California at Davis lead the floral crops experiments. Results
from tests they conducted in 2000 suggest that propargyl bromide or another
contender, iodomethane, does as good a jobor nearly soas methyl
bromide plus chloropicrin in quelling some of a flower's worst soil-dwelling
enemies.

The Davis scientists
used 20-gallon, black-plastic nursery pots as single, self-contained microplots.
Sunk into the ground at test sites and filled with local soils ranging
from light sandy loams to heavy clays, the microplots nearly replicate
conditions in commercial growers' fields.

Elmore and MacDonald used more than four dozen of these microplots, in all, for
their experiment. The study is among the first to scrutinize, in microplots, an
assortment of fumigants as possible alternatives to methyl bromide plus
chloropicrin for cut-flower production.

Elmore and MacDonald installed the handy microplots at a test site near Davis,
in northern California. They also set up other plots about 180 miles southwest
of Davis, at coastal and inland sites near Watsonville. They used a syringe to
inject candidate fumigants into the soil, mimickingat a much smaller
scale, of coursegrowers' preplant fumigation of fields.

The researchers also buried, at various depths, small nylon bags containing
spores of a notorious, soil-dwelling microbe called Fusarium oxysporum;
seeds of weed pests such as field bindweed, little mallow, or common purslane;
or species of destructive, microscopic worms called nematodes.

Other sachets contained bits of reproductive material, called propagules, of
calla lilies or gladioli. Perhaps surprisingly to home gardeners, the
reproductive pieces are, according to Elmore, as much of a nuisance as weed
seeds. "If you leave some propagules behind in the field after you harvest
your crop, and don't kill them with a fumigant," he says, "they can
sprout later and will contaminate your new crop. They may also carry over
nematodes and pathogens to the next crop." Many home gardeners, in
contrast, welcome the proliferation and spreadcalled
naturalizationof their lilies and gladioli because it saves them the work
of planting new bulbs or tubers.

The researchers color-coded the little nylon bags for easy identification of
the contents later on. They equipped each sachet with a long, nylon cord for
easy removal of the bags at specially timed intervals during the experiment.

The team applied methyl bromide plus chloropicrin in the standard 67:33 mix
that growers of cut flowers use. In other microplots, they applied propargyl
bromide at various depths and at rates ranging from 25 to 150 pounds per acre,
iodomethane at 150 or 235 pounds per acre, or metam sodium at 320 pounds per
acre.

"Although results varied somewhat from site to site," reports Elmore,
"we found that either propargyl bromide or iodomethane, applied at
moderate rates, gave control that was nearly as good as methyl bromide. None of
the chemicals knocked out field bindweed or little mallow, but that's been the
case with methyl bromide plus chloropicrin, too."

Elmore and MacDonald are repeating the tests this year. Their findings, though
carried out in Californiathe nation's leader in cut-flower
productionshould also be useful in other states where cut flowers are
grown. In 2000, America's cut-flower crop had a wholesale value of more than
$427 million.

Related work may help growers of garden roses, the kind home gardeners buy at
the nursery as potted plants or as "bare-root" plants. Plant
pathologists Sally M. Schneider and James S. Gerik, also of the ARS Water
Management Research Unit, will start a new study this year at Jackson &
Perkins' commercial garden-rose farm in Kern County, and at an ARS research
site in Parlier, near Fresno. California growers in and around Kern County
produce more than 50 percent of the nation's garden roses.

Unlike the black-plastic microplots favored by the Davis team, Schneider will
use 18-inch-diameter, 4-foot-long concrete pipes, turned on end and set into
the ground, for her microplots. Her experiment targets harmful
nematodesin particular, root-knot nematodes. They feed on roots, robbing
roses of vital carbohydrates. And the nematodes cause galls to form on roots.
Galls interfere with the roots' ability to take up water and nutrients from the
soil.